The disclosure relates to gas turbine engines. More particularly, the disclosure relates to machining of components having cast internal passageways.
Various gas turbine engine components are formed by investment casting followed by machining. Examples include cooled shrouds or blade outer air seals (BOAS). BOAS segments may be internally cooled by bleed air. For example, there may be an upstream-to-downstream array of circumferentially-extending cooling passageway legs within the BOAS segment. Cooling air may be fed into the passageway legs from the outboard (OD) side of the BOAS segment (e.g., via one or more inlet ports (inlets) at ends of the passageway legs). The cooling air may exit the legs through outlet ports (outlets). The outlets may be in the circumferential ends (matefaces) of the BOAS segment so as to be vented into the adjacent inter-segment region. The vented air may, for example, help cool adjacent BOAS segments and purge the gap to prevent gas ingestion. The outlets may also be in the longitudinal ends. The outlets may also be along the inboard (ID) side/face of the BOAS segment.
The BOAS segments may be cast via an investment casting process. In an exemplary casting process, a ceramic casting core is used to form the passageway legs. The core has legs corresponding to the passageway legs. The core legs extend between first and second end portions of the core. The core may be placed in a die. Wax may be molded in the die over the core legs to form a pattern. The pattern may be shelled (e.g., a stuccoing process to form a ceramic shell). The wax may be removed from the shell. Metal may be cast in the shell over the core. The shell and core may be destructively removed. After core removal, the core legs leave the passageway legs in the casting. The as-cast passageway legs are typically open at both circumferential ends of the raw BOAS casting. At least some of the end openings may be closed via plug welding, braze pins, or other means. The casting may be machined to provide a desired precise shape.
The air inlets to the passageway legs from the OD side of the casting may be formed during the original casting or by subsequent machining (e.g., drilling). The air outlets from the passageway legs to the ID side of the casting may similarly be formed.